The invention relates to a replay appliance for recording media containing information blocks, having means which are independent of the contents directory for access to files and information, such as video information on a hard disk, a digital versatile disk, which is also called a DVD, a CD-ROM, a floppy disk or a data tape, which have a recording format from the so-called Yellow Book.
The CD, which was originally developed as a digital recording medium for audio sequences, already has numerous successors for recording and/or replaying information stored in information blocks. However, additional items were required to allow the CD to be used as a data medium.
While, in the case of the audio CD, the data were stored in tracks and a time code was sufficient to locate the individual sectors, the sectors were given additional headers, a further error correction level and a file system for administration of the data on the disk. Much of the information, which was accommodated in the sub-channels on the conventional CD, was moved into the header. Thus, in principle, with the DVD, a change was made from addressing via sub-channels, and the size of the sectors for all types of data was limited to 2048 bytes. For data security reasons, the data on CD-ROM and DVD are not arranged physically following one another sequentially, but are distributed over the disk in data packets using a specific algorithm, which is even more complex for the DVD than for the CD-ROM. The data in each sector are arranged in rows, are interleaved and are stored on the DVD in relatively small packets, the so-called recording sectors, which are split into two blocks by means of a synchronization code. With a DVD video, this is also supplemented by copy protection and prior data reduction. Since the information is stored in so-called information blocks on the recording media, replaying by means of absolute relative time coding, in an analogous manner to a CD, is fundamentally impossible.
In principle, the information level (which is called a layer) is, however, split in a similar way to a CD into a lead-in, a program area and a lead-out. The contents directory in the case of a DVD, which has no sub-channel, is accommodated in sectors and is referred to as the so-called file system by means of which files are located on the recording medium. The file systems for applications such as the hard disk of a computer, the CD-ROM organized in accordance with ISO 9660 Standard and the DVD designed in accordance with the UDF Format have further differences.
The object of the invention is to provide a replay appliance for recording media containing information blocks, having means which are independent of the contents directory for access to files and information, for example if the contents directory or file system is damaged, even though the contents directory is not available in a sub-channel which can be reconstructed in a simple way, and differs depending on the application.
This object is achieved by means, which are specified in independent claims, and advantageous refinements and developments are specified in dependent claims.
One aspect of the invention is to allow access to important files and information despite a content directory for the file system being damaged and despite the use of different file systems.
According to the invention, a search is for this purpose carried out in blocks of the recording medium, using a characteristic feature of the file to be located. It has been found that recording media having information blocks have so-called designators, which, despite the content directory not being legible and the use of different file systems, are suitable in an advantageous manner to locate files, which need to be replayed. Even if the physical location of the designator is initially unknown owing to a defective or damaged contents directory, it is initially identified on the basis of its length, which, for example in the case of a DVD video, is generally 12 bytes, and on the basis of its position at the start of a sector or cluster. If such a designator is found, it is generally (in systems known to date) the video manager designator itself or its backup, which is designated in an identical manner as the DVDVIDEO-VMG in the case of a DVD. In order to be completely certain that this is the desired designator, further plausibility checks can be carried out, for example a check to determine whether the video manager is followed by a video title set, or a check using the end address of the video manager, which is contained in the video manager. The four bytes that follow the video manager designator describe the end address of the video manager. The value of the end address of the video manager plus one is equal to the number of 2048 byte blocks from which the video manager is composed. The length of the video manager and the first cluster number of the video manager are thus known. The cluster number is obtained from the position at which the first video manager designator is located. This position is found directly from the comparison (which is used as a search means) with the video manager designator, or as the result of the plausibility check from the backup of the video manager designator that has been found.
If the video manager were to be fragmented, the position of the video manager is then completely reconstructed using the first cluster number of the video manager and the first or second file allocation table. The term file allocation table in this case represents a pointer, which points to the number of the block, which contains the associated information. The first and second file allocation tables are identical, so that the redundancy provided in this way ensures adequate confidence for finding fragmented information blocks.
In the case of a DVD-ROM or a DVD movie which, as a rule, are not fragmented, the circuitous route via a file allocation table is superfluous, since the position of the video manager is already completely known immediately once the first memory block of the video manager has been found.
Once the contents directory which is contained in the video manager has been reconstructed in this way, the recording medium can then be played back completely, even if the file system or contents directory is damaged.
The information corresponding to the contents directory of the recording medium is reconstructed in an advantageous manner, making it possible to replay information media which have faults relating to the contents directory, which is otherwise absolutely essential for replaying. With a replay appliance designed in such a way, it is then possible not only to replay recording media having different file systems, but also to replay recording media having a damaged content directory.